Genes for direct methylation of glycine provide high levels of glycinebetaine and abiotic-stress tolerance in Synechococcus and Arabidopsis

Abstract

Betaine is an important osmoprotectant, synthesized by many plants in response to abiotic stresses. Almost all known biosynthetic pathways of betaine are two-step oxidations of choline. Recently, a biosynthetic pathway of betaine from glycine, catalyzed by two N-methyltransferase enzymes, was found. Here, the potential role of N-methyltransferase genes for betaine synthesis was examined in a freshwater cyanobacterium, Synechococcus sp. PCC 7942, and in Arabidopsis plants. It was found that the coexpression of N-methyltransferase genes in Synechococcus caused accumulation of a significant amount of betaine and conferred salt tolerance to a freshwater cyanobacterium sufficient for it to become capable of growth in seawater. Arabidopsis plants expressing N-methyltransferase genes also accumulated betaine to a high level in roots, stems, leaves, and flowers and improved seed yield under stress conditions. Betaine levels were higher than those produced by choline-oxidizing enzymes. These results demonstrate the usefulness of glycine N-methyltransferase genes for the improvement of abiotic stress tolerance in crop plants.cyanobacteria ͉ methyltransferase ͉ osmoprotectant ͉ stress resistance T oday, Ϸ20% of the world's cultivated land and nearly half of all irrigated lands are affected by high salinity (1). High salinity causes ion imbalance and hyperosmotic stress in plants. Organisms that thrive in hypersaline environments possess specific mechanisms for the adjustment of their internal osmotic status. One such mechanism is the ability to accumulate low-molecular-weight organic-compatible solutes such as sugars, some amino acids, and quaternary ammonium compounds (2-4). Glycine betaine (N,N,Ntrimethylglycine, hereafter betaine) is a major osmolyte (2-4). Another mechanism for adaptation to high salinity is the exclusion of the Na ϩ ion from sodium-sensitive sites (5). Genetic engineering techniques have been applied to improve the salt tolerance of plants (6-13). Considerable success has been demonstrated by manipulating the Na ϩ ͞H ϩ antiporter genes (6-8). By contrast, the genetic engineering of betaine synthesis has been hampered by low accumulation levels of betaine (9-13). Most known biosynthetic pathways of betaine include a two-step oxidation of choline: choline 3 betaine aldehyde 3 betaine. The first step is catalyzed by choline monooxygenase (CMO) in plants (14), choline dehydrogenase (CDH) in animals and bacteria (15,16), and choline oxidase in some bacteria (11,17). The second step is catalyzed by NAD ϩ -dependent betaine aldehyde dehydrogenase in all organisms (15,18,19), although in some bacteria, CDH and choline oxidase also catalyze the second step (15-17). Hitherto, all attempts at betaine synthesis have been carried out by using choline-oxidizing enzymes (9-13). The supply and transport of betaine precursors such as choline, ethanolamine, and serine to plastids may be of importance, because these precursors have been suggested to be limiting (12,13).Recently, we showed that a halotolerant cyanobacter...

Global plant-responding mechanisms to salt stress: physiological and molecular levels and implications in biotechnology

“…For example, over expression of the syntheses genes of Pro and GB can improve the content of Pro and GB obviously and endow the transgenic plants with enhanced tolerance (Kavi et al, 1995;Waditee et al, 2005). Similarly, the transgenic plants with more SOS1 or NHX1 transporters are able to regulate ion transport more quickly and effectively to grow well under salt stress (Liu et al, 2000;Quintero et al, 2002;Yang et al, 2009).…”

“…In view of its powerful features, transgenic engineering was also employed to operate the GB concentration. Transgenic Arabidopsis expressing the N-methyltransferase gene, which is one of the three key enzymes in GB synthesis, possess improved seed yield compared to the control under salt stress (Waditee et al, 2005). Similarly, overexpression of GOLS2, a GB synthase, enhanced tolerance to high salinity in Arabidopsis (Sun et al, 2013).…”

Glycine betaine mediated disease resistance against Sclerospora graminicola in Pearl Millet

“…In higher plants, GB is synthesized from choline by two-step oxidation reactions that are catalyzed by choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH) respectively [9]. Beside, a biosynthetic pathway of GB from glycine by the activity of two N-methyl transferase enzymes has recently been reported [10].…”

Proteomic Analysis of a Sea-Ice Diatom: Salinity Acclimation Provides New Insight into the Dimethylsulfoniopropionate Production Pathway

“…Two of the elevated SAMmt protein spots were different charge forms of Fc212856, a putative SAMmt with similarity to sarcosine dimethyl-Gly methyltransferase. Sarcosine dimethyl-Gly methyltransferase is an alternate synthesis pathway for the osmolyte Gly betaine that does not produce hydrogen peroxide as a by-product like the traditional choline oxidase pathway (Waditee et al, 2005). Substrates for the third SAMmt protein spot (Fc207357, relative protein abundance elevated 2.8-fold and transcripts elevated 10-to 15-fold in high-salinity/DMSP conditions) have not been characterized.…”